must need may can用must提问的句子 比如 must we put up a sign by the riverside?回答应该用那个情态动词还有这一系列的情态动词
问题描述：
must need may can
用must提问的句子 比如 must we put up a sign by the riverside?
回答应该用那个情态动词
还有这一系列的情态动词
答
must用needn't
need用needn't
may用may not或must not
can用can't